Commit a5003fc04113 ("[ALSA] emu10k1 - simplify page allocation for synth")switched from using the DMA allocator for synth DMA pages to manuallycalling alloc_page().However, this usage has an implicit assumption that the DMA address spacefor the emu10k1-family chip is the same as the CPU physical address spacewhich is not true for a system with a IOMMU.

Since this made the synth part of the driver non-functional on such systemslet's effectively revert that commit (while keeping the__synth_free_pages() simplification).